1. Field of the Invention
The invention relates to blow molding machines of the type having a continuously extruded parison at one station and one or more pairs of mold halves which periodically transfer an extruded parison to a blow molding station where it is acted upon by a blow pin. The invention is particularly concerned with the control means for such blow molding machines which will be activated in the event of depletion of plastic material in the extruder, or if it is desired to "dry cycle" the machine for observation, test or adjustment purposes.
2. Description of the Prior Art
It is known to have sensing means such as an infrared detector at the parison station at such machines which will signal the arrival of the bottom of each descending parison at a predetermined location in order to exhaust a product at the blow molding station, after which the mold halves will open and be transferred back to the parison station to pick up the next parison. Huncar Laboratories, Inc. of Cincinnati, Ohio has a system where a photocell detects the descent of a parison and matches its speed against a timer, slowing down or speeding up the extruder depending upon the parison speed. However, in previously known systems, if the extruder ran out of material or was shut off, the machine would continue to run, which could cause waste and possibly damage or injury.